In order to protect an occupant at the time of vehicle collision or emergency, there is widely used a side airbag device to protect the occupant from a side with air chambers formed in an airbag for mainly protecting the chest, the abdomen, and the lumbar of the occupant by inflating and deploying the airbag between the inner sidewall of a vehicle and the occupant. In such a side airbag device, it is necessary to keep an inner pressure (a gas pressure) high by quickly inflating and deploying an air chamber for a lumbar in the airbag particularly in order to inhibit an occupant from moving toward the collision side and secure a space for deploying the airbag, at the time of side collision.
Therefore, an airbag device of supplying a gas to lower and upper air chambers in an airbag through a gas distributor, making the size of the outlet port of the gas distributor for the lower chamber to supply the gas to the lower chamber for a lumbar larger than the size of the outlet port for the upper chamber, disposing a check valve to prevent the gas from flowing from the lower chamber to the upper chamber, inflating and deploying the lower chamber quickly, and keeping the pressure of the lower chamber high has heretofore been known (refer to Patent Literature 1).
With such a conventional airbag device, however, the outlet port of the gas distributor for the lower chamber is extended toward the side of the lower chamber, the check valve is formed with the extended part, and, when an occupant hits the lower chamber and a gas flows from the lower chamber to the upper chamber, the extended part comes close together in the manner of closing the lower chamber outlet port and the gas is prevented from flowing out. Therefore, with the airbag device, the lower chamber outlet port begins to close after the lower chamber inflates and then, the lumbar of the moving occupant is received by the lower chamber. As a result, undesirably, the start of the closing operation of the lower chamber outlet port and the sealing of the lower chamber by the closure may be delayed and the inner pressure of the lower chamber may lower by then. Furthermore, with the airbag device, the gas distributor is formed with a cloth wrapped in a cylindrical shape and, when the lower chamber inflates, the outer circumferential surface sticks to both the separating surfaces of the airbag and the lower chamber outlet port expands in the same way as the airbag. Consequently, the lower chamber outlet port, although how it closes is not obvious, starts to close gradually from a cylindrically expanded state after an occupant hits the lower chamber, hence it takes time until it is closed, and the sealing of the inflated lower chamber and the transfer to a state of being capable of maintaining the inner pressure may be delayed undesirably.